1. Field of the Invention
The present invention relates to a vehicle-mounted antenna system to be mounted on the inside of a window glass of a vehicle or the like, and in particular, to a wiring structure of a feeder line which electrically connects a radiating conductor formed on an inner surface of a glass plate with a circuit board accommodated in a housing.
2. Description of the Related Art
Conventionally, there is known a vehicle-mounted antenna system in which a radiating conductor is formed on an inner surface of a rear glass or a front glass of a vehicle which faces the interior of the vehicle and an electronic circuit unit including a pre-amplifying circuit is attached to the inner surface, thereby allowing reception of circularly polarized waves, linearly polarized waves or the like transmitted from satellites or ground-based stations. This type of antenna system has advantages that the service life of the system can be extended and the risk of theft can be lessened, as compared to vehicle-mounted antenna systems installed outside vehicles such as roofs. Further, the antenna system also has an advantage that the size is small which allows wider viewing angles, even as compared to antenna systems set in the vicinity of a window glass inside the vehicle.
In this type of vehicle-mounted antenna system, an electronic circuit unit attached on an inner surface of a glass plate, such as a rear glass or a front glass, which faces the interior of a vehicle, is substantially constructed such that a circuit board provided with a pre-amplifying circuit and the like is accommodated in a housing. Also, a predetermined shape of a radiating conductor formed on the glass plate is electrically connected to the circuit board by an appropriate means so that the radiating conductor is supplied with power or supplied with signals.
As a conventional example, a vehicle-mounted antenna system of a construction in which a conductor piece is caused to protrude from an insulating housing which accommodates a circuit board, and the conductor piece is soldered to a feeding point of a radiating conductor is suggested (Japanese Unexamined Patent Application Publication No. 6-53722 (Pages 2 and 3, FIG. 1)). Since one end of the conductor piece is connected to an input part of a pre-amplifying circuit inside the housing, an electrical connection between the radiating conductor and the pre-amplifying circuit can be established by the conductor piece and the electronic circuit unit can be fixed to the glass plate.
The aforementioned conventional example is a vehicle-mounted antenna system in which power is fed to the radiating conductor by the conductor piece protruding from the housing of the electronic circuit unit. Since this antenna system is easily subjected to the influence of extraneous noises, there is a problem in that the reliability of the antenna system is lowered. Thus, a structure in which a feeder line which is not readily affected by the extraneous noises is connected to the radiating conductor can be taken into consideration. However, another problem occurs in which the attenuation of signals may increase if the feeder line connected to the feeding point of the radiating conductor is not efficiently led along a predetermined path.
As in the conventional example, in the case of an antenna system in which the electronic circuit unit as an integral part is fixed to the glass plate by soldering or the like, there is also a problem in that maintenance is not easy because of the complexity for removing the electronic circuit unit from the glass plate or attaching it thereto.